1. Field of the Invention
The present invention relates to an electric power steering system.
2. Description of Related Art
Various electric power steering systems have been developed in which rotation of an output shaft of an electric motor is transmitted to an input shaft (worm shaft) of a speed reducer via a coupling (see, for example, Japanese Patent Application Publication No. 2008-290693 (JP 2008-290693 A), Japanese Patent Application Publication No. 2009-280191 (JP 2009-280191 A), and Japanese Patent Application Publication No. 2009-286387 (JP 2009-286387 A)).
Couplings in JP 2009-280191 A and JP 2009-286387 A include an annular body portion and a plurality of protruding portions. The body portion has a motor shaft hole in a center thereof. The protruding portions protrude radially from the body portion. An elastic protrusion is formed on each of the protruding portions to apply an urging force to the worm shaft in an axial direction thereof. However, the elastic protrusions are arranged away from a shaft center of the worm shaft, leading to a high moment load.
Thus, a spacer may be interposed between the worm shaft and the motor shaft to urge the shaft center of the worm shaft in an axial direction thereof, and arranged in the body portion of the coupling.
However, in this case, assembly of the electric power steering system needs an operation of assembling the two components, the coupling and the spacer, to the system. This may hinder the electric power steering system from being easily and efficiently assembled.